Compositions for the production of light gypsum, which contain as key components particulate setting gypsum, more particularly in the form of anhydride and/or hemihydrate, and at least one blowing agent consisting of an acid in the form of a mineral acid or an organic acid and, as an additional component, a gas-forming salt, are already known. In the context of the present invention, gypsum in anhydride form is understood to be pure calcium sulfate with no water of hydration.
Thus, CA 119:78617, an abstract of JP-A-05105544, relates to a low-density gypsum product in which anhydrite, sulfates and calcium carbonate are contacted with one another, resulting in the formation of carbon dioxide gas bubbles.
CA 91:61734, an abstract of SU 77-2522229, relates to a low-density gypsum product in which gypsum hemihydrate is reacted with a sodium carbonate melt, sodium sulfate and water.
CA 89:48101, an abstract of JP-A-76-92941, relates to a low-density gypsum product in sheet form which is obtained by reacting gypsum hemihydrate together with calcium carbonate in the presence of dilute sulfuric acid and water.
CA 85:24916, an abstract of JP-A-74-107006, relates to a low-density gypsum product, in which a gypsum hemihydrate is reacted together with a powder-form alkali metal or alkaline earth metal carbonate in the presence of an aqueous solution additionally containing methyl cellulose. The foamed material thus produced has a density of 0.5 g/cm.sup.3.
CA 84:168779 relates to a gypsum suspension containing calcined gypsum, calcium carbonate and a 40% hexafluorosilicic acid and, for the rest, water. A light gypsum with a density of 0.55 is obtained in this way.
CA 84:154766, an abstract of JP-A-74-77409, relates to a low-density gypsum product, in which a calcined gypsum is contacted with sodium stearate, calcium carbonate, dilute hydrofluoric acid and, for the rest, water and then reacted to form foamed mouldings. The light gypsum mouldings obtained in this way have a density of 0.61.
CA 84:154755, an abstract of JP-A-74-66659, relates to a low-density gypsum product, in which a mixture of 95% by weight calcium sulfate hemihydrate and 5% by weight calcium carbonate is reacted with a 3% sulfuric acid, fibrous material. The mouldings obtained have a specific gravity of less than 0.1.
CA 84:126033, an abstract of JP-A-74-64062, relates to a low-density gypsum product, in which calcined gypsum is reacted together with calcium stearate, calcium carbonate and a 40% aqueous hexafluorosilicic acid solution and water to obtain a molded product having a specific gravity of 0.47.
CA 82:47224, an abstract of JP-A-71-119764, relates to a low-density gypsum product, in which a calcined gypsum is reacted together with water, calcium carbonate, calcium fluorosilicate and barium stearate. A calcined gypsum product with a density of 0.57 g/cm.sup.3 is obtained in this way.
CA 80:73793, an abstract of JP-A-72-5988, relates to a low-density building material, in which a carbonate or bicarbonate is reacted with a phosphoric acid partial ester at room temperature or above room temperature. Gypsum inter alia may be added to this mixture which, if heated to 50.degree. C., leads to a foamed gypsum product with a density of 0.4 g/cm.sup.3.
CA 122:272364, an abstract of German patent 43 33 115, relates to cement, concrete or a similar building material which is obtained by reacting a curable calcium sulfate together with an alkali metal bicarbonate, boric acid, calcium hydroxide and a foaming agent, a plasticizer and a retarding agent. The low-density gypsum products obtained in this way have a density of 1.3 g/cm.sup.3.
CA 120:84826, an abstract of EP-A-562651, relates to a gypsum product with an apparent density of 0.5 to 1.5 g/cm.sup.3 which is obtainable by reacting calcium sulfate, magnesium hexafluorosilicate, aluminium stearate, calcium carbonate and/or magnesium carbonate, methyl cellulose, sodium citrate and water.
Research Disclosure, Vol.135, July 1975, page 37, Disclosure No. 13540, relates to the production of low-density gypsum, in which gypsum hemihydrate is first suspended together with manganese dioxide and water and hydrogen peroxide is added to the resulting suspension for foaming. In addition, PVA emulsions may be added to this product to improve its properties.
CA 101:11552, an abstract of JP-A-82-124909, relates to a low-density gypsum product in which a gypsum hemihydrate is reacted with barium stearate, calcium carbonate, calcium oxide, an aqueous polyvinyl alcohol solution and water. Gypsum elements with a density of 0.76 are obtained in this way.
CA 101:11551, an abstract of JP-A-82-124910, relates to a low-density gypsum product, in which .beta.-gypsum hemihydrate, calcium stearate, calcium carbonate, calcium oxide, polyvinyl alcohol and ammonium sulfate are reacted with hexafluorosilicic acid. The product thus obtained has a density of 0.78.
CA 101:11550, an abstract of JP-A-82-124908, relates to a gypsum product with a density above 0.76 obtained by reacting gypsum hemihydrate, hydrophobic stearates, carbonates or bicarbonates and basic oxides in the presence of acidic fluorides and water and synthetic resins.
CA 101:11549, an abstract of JP-A-82-124907, relates to a low-density gypsum product, i.e. a gypsum product with a density of about 0.78, obtained by reacting gypsum hemihydrate, hydrophobic stearates, carbonates or bicarbonates, basic oxides, emulsions of synthetic resins, water and acid fluorides, such as aqueous hexafluorosilicic acid.
CA 100:214666, an abstract of JP-82-112342, relates to a gypsum product with a density of about 0.78 obtainable by reacting gypsum hemihydrate, stearates, carbonates or bicarbonates, basic oxides, acidic fluorides, for example hexafluorosilicic acid, in the presence of polyvinyl alcohol.
CA 89:151558, an abstract of JP-A-76-128274, relates to a gypsum product with a density of 0.35 g/cm.sup.3, in which a calcined gypsum, a fibrous material, a metal oxide and a stabilizer are contacted with water, a percarbonate is added and the mixture as a whole is then subjected to a heat treatment.
CA 87:89532, an abstract of JP-A-75-93352, relates to a low-density gypsum product in which an .alpha.-gypsum is stirred together with water and ammonium hydrogen carbonate is then added.
CA 80:86931, an abstract of JP-A-69-84902, relates to a gypsum product with a density of about 0.56 g/cm.sup.3 obtainable by reacting a calcined gypsum suspension to which a concentrated aqueous formaldehyde solution, water and ammonium hydrogen carbonate are added.
CA 82:102462, an abstract of JP-A-72-347, relates to a low-density gypsum product obtainable by reacting synthetic gypsum and sodium hydrogen carbonate to which a 1% polyvinyl alcohol solution was added before heating for 1 hour to 80.degree. C.
CA 81:175233, an abstract of JP-A-72-107634, relates to gypsum products with densities of 0.15 to 0.65 g/cm.sup.3 obtainable by reacting a gypsum suspension together with a fatty acid salt, a foam stabilizer based on a fatty acid salt, calcium carbonate and aluminium sulfate.
CA 115:238433 and CA 112:164011 an abstract of an Article in CLC Chem. Labor. Biotech. (1990), 41 (2), pages 79-80, relates to an artificial building material, in which surfactants, barium carbonate and water are mixed and foamed and clay or inter alia gypsum is mixed with the resulting foam.
JP-A-901296780 relates to a low-density gypsum product or gypsum foam obtained by reacting a gypsum suspension with a sulfonate of a C.sub.10-16 fatty acid alkyl ester as foaming agent.
DE-C-41 34 550 relates to a process for the production of in situ foam by reacting suspended gypsum with polyisocyanate prepolymers, in which 30 to 70% by weight of gypsum dihydrate and 30 to 30% of water, based on the slurries, are used as the suspended gypsum and 40 to 60% by weight of the gypsum dihydrate/water slurries and 60 to 40% by weight of standard diphenyl methane-4,4'-diisocyanate or diphenylmethane-4,2'-diisocyanate prepolymers with an NCO content of 2 to 20% by weight or 2,4-toluene diisocyanate or 2,6-toluene diisocyanate prepolymers with an NCO content of 2 to 20% by weight or a mixture of these compounds are introduced into the gap and left to cure at normal temperature and pressure. The in situ foam is produced in particular by means of a multicomponent unit, such as a spray can or spray gun. In the case of two-component systems, the aqueous component consists of a thixotropic hydrargillite/REA gypsum (REA gypsum=gypsum from flue glas desulfurizing plants) mixture with a solids content of at least 66% by weight using water-soluble, chemically modified celluloses as the thixotropicizing agent. The foam thus obtained can be machined after curing and is flame-retarded. WO 93/08142 is based on the same priority.
CA 92:63584p, an abstract of JP-A 79/119528, relates to a low-density gypsum product, in which a gypsum hemihydrate is foamed with a urethane prepolymer and water, optionally in the presence of fillers, and allowed to cure. A flame-retardant gypsum product with a specific gravity of 0.52 is obtained in this way.
In view of the steadily intensifying environmental debate, there is a high demand for more environmentally compatible insulating materials and low-density gypsum parts and gypsum mouldings.
Modern one-component and two-component polyurethane foams, which are used in containers, such as cans, or with mixing units, inter alia for heat insulation, harm the environment with some of their ingredients, for example the Frigen.RTM. used as blowing agent, i.e. fluorochlorocarbons, partly halogenated fluorochlorocarbons, fluorocarbons (CFCs, HCFCs, FCs), and continue to harm the environment through halogen-containing flameproofing agents.
All the above-mentioned compositions for the production of low-density gypsum have disadvantages insofar as, in the case of polyurethane-free systems, foaming by gas generation takes place immediately after addition of the gas-generating component, i.e. the pot life or induction time (=time before the increase in volume) of such systems is of the order of 1 to 10 seconds which makes systems of the type in question difficult to handle in practice for direct "in situ mixing". However, even with systems containing polyisocyanates, which normally have pot lives or induction times of 5 to 60 seconds in the case of pure PU foams, this period of time is generally not sufficient to enable such a known composition to be introduced before foaming into complicated spaces where it is used as a in-situ foam (cf. Franck, Kunststoff-Kompendium, 1st Edition, Wurzburg 1984, page 211). Even the rise time (=time from the beginning of mixing to the end of expansion) of pure PUR foams is only 55 to 270 seconds and, accordingly, in complicated and large spaces, can never lead to a light gypsum which is uniformly foamed--a crucial requirement, for example, for good insulating properties.